This section provides background information related to the present disclosure which is not necessarily prior art.
Load monitoring is performed in a variety of industries and applications as a method of predicting maintenance needs, for controlling motors, and for precise load measurements. Strain gage load cells are commonly used for these load measurements as they provide accurate data over a wide range of loads. Challenges arise with the use of these load cells due to the need to connect wires to the load cell in order to both power the strain gauges and to send the data back to a data acquisition system. In many applications, wires are difficult and time consuming to install, and, particularly in dynamic systems and in applications located in harsh environments, the wires are prone to breaking. For this reason, and due to the improvements to wireless communications over the past several years, wireless load cells have emerged.
Existing wireless load cell assemblies, however, have other drawbacks when incorporating them in to certain applications. Most require installation at a specific orientation, so as to ensure communications with a base system. In order to maintain this rotational positioning throughout the life of the system, these load cell assemblies incorporate an anti-rotation coupler, which requires a housing, poses installation challenges to achieve proper orientation, allows for uneven wear of the load cell spool, and increases load cell manufacturing complexity. In addition, existing wireless load cells have a relatively high current draw of greater than 6 mA at 60 Hz. These devices must be powered from a power storage device, such as a battery, that is sufficiently small in size to be packaged with the load cell. The high current draw combined with a small power storage device requires that the storage device be replaced frequently, every 3 months for example, which may be impractical for applications that are difficult to physically access. In addition, these systems have mono-directional communication systems, meaning that data can be transmitted from the load cell assembly to a base unit, but the load cell cannot receive information back from a base unit. Furthermore, existing wireless load cells are limited to measuring load only, and do not have the capability of measuring additional system data such as velocity, acceleration, position and temperature.
One example application of a use of a wireless load cell is on a pumpjack system used in the oil industry. Pumpjacks are dynamic systems used to pump fluid out of a well. Typically, these systems may have separate assemblies and controllers to measure and control characteristics of pumpjack equipment including measuring the speed at which the system is pumping, turning the pump on or off based on the weight of the fluid in the production tubing, or a combination of characteristics, such as measuring the weight of the fluid in the production tubing and the location of the polished rod relative to ground level. Measuring and controlling these characteristics are important for efficiency, health monitoring, and safety of the pumpjack. If the characteristics are not monitored properly, damage can be caused to parts of the pumpjack. For instance, the pumpjack can be damaged if its tube is only partially filled.
In measuring these characteristics, it is sometimes desirable to obtain high frequency data for improved diagnostics, in the event an anomaly occurs. For example, if there is a sudden change in load, it can be helpful to record the surrounding data at a high frequency, to aid in pinpointing the cause of the spike, and to determine whether or not it is a potential issue. Furthermore, it is desirable to monitor multiple characteristics of a pumpjack system for a predictive maintenance procedure for the system.
Some pumpjack systems currently use either wired or wireless load cell assemblies installed on a polished rod of the pumpjack system to measure the load on the rod. These load cell assemblies are continuously exposed to the elements and are often located in remote areas. The wired load cell assemblies are costly and time intensive to install, and have large maintenance costs due to the need to repair broken wires. In the past, however, wireless load cell assemblies have been cost prohibitive and unreliable due to RF drop outs during communications. Both wired and wireless load cell assemblies have only provided load data at a set frequency, and have not been capable of providing a full set of pumpjack operating characteristics, such as velocity and position, that are needed for optimal control and diagnostics.
Thus, there is a need for improved wireless load cell assemblies that do not require rotational positioning, that can last for several years without the need to change batteries, and that are capable of bi-directional communications.